It is common practice to recirculate water in a swimming pool for filtration and aeration and, if desired, for heating. It is also common practice, and in fact imperative, to treat the water with a sanitizing agent to kill pathogenic bacteria.
The most widely used technique for sanitizing swimming pool water is to periodically add concentrated chlorine or sodium hypochlorite, the aqueous solutions of which are effective bactericides. However, dilute aqueous solutions tend to decompose on exposure to sunlight and contact with metals, such as copper. Since it is desirable to maintain available chlorine at levels between 0.4 to 1.5 parts per million (ppm) and to keep the pH at a level of about 7 to 8, it becomes necessary to add many times this amount of available chlorine in the course of a sunny day.
In order to stabilize the free chlorine in pool water, cyanurates or other materials may be added, but there is still a need to continually check the swimming pool and periodically add liquid chlorine. This procedure of checking and adding liquid chlorine must usually be repeated on a weekly basis.
Stabilized chlorine tablets in cartridges which float on the surface of the swimming pool have come into popular use by home owners who maintain their own swimming pools because it is then necessary to simply check the cartridge and replace it or refill it when all the chlorine tablets have been dissolved. Maintaining the chlorination of the water is then much less of a chore. Periodic checking of the chlorine level is reduced from weekly to about monthly or longer periods depending upon such factors as usage and water temperature besides average daily sun exposure. However, chlorine tablets generally leave a residue in the water which builds up in time and is not believed to be as effective as an aqueous solution of a chlorine-based oxidant, such as chlorine sodium hypochlorite or chlorinated sodium isocyanurate, for example, all of which aqueous solutions are referred to hereinafter as a liquid sanitizing agent, although the preferred liquid sanitizing agent is sodium hypochlorite with sodium isocyanurate added.
Professional pool maintenance personnel prefer to use a liquid sanitizing agents, and homeowners who maintain their own swimming pools would also prefer to use liquid sanitizing agents, but both would rather be free of the need to add liquid sanitizing agents on such a frequent basis as once a day, or even once a week. The liquid sanitizing agents are usually poured from a jug while standing beside the pool, with the result that water with a high concentration of the liquid frequently splashes on clothing, thus seriously damaging the clothing.